1. Field of the Invention
The present invention relates to a process and an apparatus for the production of a metallic honeycomb body, for supporting a catalyst, for use in a catalytic converter for the purification of an exhaust gas discharged from an internal combustion engine and in a catalytic converter in a chemical plant.
2. Description of the Prior Art
In recent years, a catalytic converter using a metallic honeycomb body as a catalyst carrier, constituted by a stack of metallic foils, has become adopted, for example, in the purification of an exhaust gas discharged from internal combustion engines, particularly automobiles. In this case, as shown in FIGS. 6 (A) and (B), a metallic flat foil b and a metallic corrugated foil c, with the flat foil and the corrugated foil stacked on top of the other, are spirally wound on a winding shaft a, thereby forming a honeycomb body e having a large number of through holes o in the direction of the winding shaft, and the honeycomb body e thus obtained is then fitted into a metallic casing d to form a cylindrical metallic carrier f.
In the production of the metallic honeycomb body e, in order that the structural strength is ensured to realize stabilized catalyst carrier functions, it is common practice to braze the flat foil b and the corrugated foil c, constituting the metallic honeycomb body e, to the casing d, thereby integrating the metallic honeycomb body e with the casing d.
An example of conventional methods for joining a flat foil b to a corrugated foil c in the production of a metallic honeycomb body e comprises winding a flat foil b and a corrugated foil c with the flat foil and the corrugated foil stacked on top of the other, fixing the outermost circumferential end of the flat foil b, press-fitting the resultant spiral into a metallic casing d, spreading a powdery brazing metal in the interior of the assembly, heating the assembly to deposit the powdery brazing metal between the corrugated foil and the flat foil and between the metallic honeycomb body and the metallic casing, thereby joining the corrugated foil to the flat foil and, at the same time, joining the metallic honeycomb body to the metallic casing.
This method, however, is disadvantageous in that it is difficult to surely spread and deposit the powdery brazing metal at the sites to be joined, a sure and stable joint cannot be provided, and the cost of the powdery brazing metal is high.
In order to solve these problems, for example, another jointing method, as shown in FIG. 7, has been proposed. This method comprises providing a brazing foil g, which has been previously cut into a very small piece, for example, a piece having an approximate size of 0.05 mm in thickness.times.1 mm in width.times.12 mm in length, at predetermined intervals on predetermined positions of the flat foil, connecting the flat foil b and the corrugated foil c to a winding shaft a, which serves also as an electrode, winding them, with the flat foil b and the corrugated foil c stacked on top of the other, on the winding shaft a to form a honeycomb body e having a predetermined dimension, fixing the outermost circumferential end of the flat foil b, fitting the honeycomb body into a metallic casing, and heating the assembly in a vacuum furnace to melt the brazing foil to join the flat foil b, the corrugated foil c, and the metallic casing d to one another.
In the production of a cylindrical metallic honeycomb body e by this method, however, since the wave height and pitch of the corrugated foil c vary, the relative position of the cut brazing foils g varies even when winding is carried out under constant conditions, so that, in some cases, the joint sites between the flat foil b, the corrugated foil c and the metallic casing d are often shifted from a predetermined joint site region.
The brazing foil g used herein functions to join the flat foil b, the corrugated foil c, and the metallic casing d to one another. When the metallic honeycomb body e is incorporated into an electric heating type catalytic converter to permit a current to flow across the winding shaft a and the metallic casing d to heat the metallic foils per se, thereby enabling the temperature of the metallic honeycomb body to be raised to the catalytic activation temperature in a short time, the brazing foil g functions also to form joints which can be energized.
For this reason, the shift of the sites of joints by the brazing foil from the predetermined region gives rise to problems such as lowered joint strength, deviation of a heat pattern created by energization to cause a failure of heat to be generated, leading to a deterioration in the above functions of the metallic honeycomb body and a lowering in dimensional accuracy. This in turn results in lowered yield of acceptable honeycomb body products and, hence, lowers the productivity of the metallic honeycomb body (see Japanese Unexamined Patent Publication (Kokai) No. 179939/1993).